(1) Field of the Invention
The present invention generally relates to the field of electronic circuits. More specifically, the present invention relates to charging circuits in imaging systems.
(2) Background Information
Cameras that utilize photoflashes typically include a charging circuit that charges a photoflash capacitor included in the camera. The photoflash capacitor stores energy in the form of electrical charge. This energy is later utilized by the photoflash to produce a "flash" when a picture is taken.
Charging circuits are typically powered by a battery that provides the charging circuit's voltage and current needs. While portable film cameras, do not include various electronic circuits that utilize current and voltage from the battery, contemporary cameras include various electronic circuits other than charging circuits, that utilize power from the battery. Such electronic circuits may include microcontrollers, image sensor arrays, etc. To function properly, these electronic circuits require a minimum voltage or current supplied thereto to function properly.
According to one embodiment of a camera with a charging circuit, a battery supplies a current at a certain voltage to a step-up transformer, that is part of the charging circuit. The transformer transforms a voltage of approximately 3 volts (the battery's voltage) to a voltage of 300 volts at which the photoflash capacitor is charged. The photoflash capacitor then provides the energy stored thereon to a trigger circuit that, among other things, contributes to stepping up the voltage on the photoflash (flash tube) to about 4000 volts. This voltage causes ionization of the gas inside the flash tube. When the photoflash is triggered, the discharge of the photoflash capacitor through the ionized flash tube generates a very high current therethrough thereby causing light in the flash tube.
Alkaline batteries have started to be increasingly used in cameras due to their relatively inexpensive cost and widespread use. However, because an alkaline battery has a high output impedance and a low voltage, when the current generated by the battery rises it causes the voltage on the battery to severely drop to levels that are unacceptable to other electronic circuits in the camera. Rises in the battery current are typically caused by the transformer during the charging of the photoflash capacitor. The drop in the voltage on the battery due to the rise in current may cause malfunctions in the other electronic circuits, in the camera, that share the same battery. This problem becomes more critical when the number of batteries utilized is minimized to reduce the weight of the camera. Another problem associated with alkaline batteries is that if an excessive current draws out of these batteries, these batteries may deteriorate, thereby shortening the battery's life.
It is desirable to provide an imaging system such as a camera that may use alkaline batteries or other similar sources of power that do not cause problems to the functioning of other circuits that share the same battery/batteries. It is desirable to provide an imaging system and a method that may detect instances when the voltage of the battery/batteries reaches a certain predetermined voltage value, at which other circuits connected to the battery may malfunction, and that prevent the voltage on the battery/batteries from further dropping below the predetermined value. It is desirable to provide an imaging system and a method that may detect instances when the battery current exceeds a certain predetermined value and that prevent the battery current from further raising.